Xact3D buyer’s guide

How we score diamonds

Every diamond on Xact3D gets one score out of 100. It sums up how beautiful the stone is likely to look, based on its cut, colour and clarity, and on how those show at its size and shape.

This guide explains what goes into the score, what the numbers on a certificate mean, and what to look for in each shape. At the end you can check any diamond yourself.

The Xact3D Score is our own assessment, based on our experience as diamond wholesalers and on published cut, colour and clarity guidelines. It is not a laboratory grade. Always rely on the diamond’s grading certificate.

The Xact3D Score

One score, three parts

Cut45%

How well the stone handles light. It matters most, because a well-cut diamond looks bigger, brighter and livelier.

Colour30%

How white the stone looks for its size and shape. Larger stones and fancy shapes show colour more.

Clarity25%

Whether inclusions are visible, judged against what you can actually see at that size.

A weak area pulls the score down more than strong areas push it up, so a dark, badly cut stone can’t hide behind a perfect colour grade. If any part is rated Poor, the overall score can’t go above 59.

What the colours mean

93–100Excellent80–92Very Good60–79Good38–59Fair0–37Poor

No score? Some certificates leave out details we need, such as the depth or the polish grade. We still rate every value that is there, but we don’t give an overall score from incomplete data, and we tell you what is missing. Rare shapes (old European cuts, rose cuts, kites…) and fancy-colour diamonds are not scored.

Part 1 · Cut

What to look for on the certificate

Table %

The flat top facet, as a percentage of the stone’s width. Too big and the stone loses fire (the coloured flashes). Too small and it looks smaller and less bright.

Depth %

Total height divided by width, the most important number for fancy shapes. Too deep and the diamond hides its weight underneath, looks smaller and often shows a dark “bow-tie” across the middle. Too shallow and light leaks out the bottom, leaving a glassy “window”.

L/W ratio

Length divided by width. It sets the outline: how slim an oval is, how long a pear is. Partly a matter of taste, but the extremes look stubby or stretched.

Girdle

The thin edge around the widest point. Extremely thin edges chip easily; very thick ones add weight (and price) you can’t see from the top. It counts when the certificate reports it.

Polish & symmetry

How precisely the facets were finished and aligned. Look for Excellent or Very Good. On fancy shapes, good symmetry keeps the outline even and the sparkle balanced.

Culet

The tip at the bottom. We show it but don’t count it: most lab-grown certificates leave it out, and step cuts (emerald, asscher) end in a line rather than a point.

Cut · shape by shape

The sweet spot for each shape

Each shape is cut differently, so the ideal numbers change. These are the ranges that earn our top “Excellent” rating, and the point where a stone starts to look clearly worse.

Round

Table: 53–58%
Depth: 59–62.3%
L/W ratio: 1–1.01
Crown angle: 34–34.9°
Pavilion angle: 40.6–41°

Avoid: table below 50% or above 69%, depth below 56.5% or above 65%

Oval

Table: 53–63%
Depth: 58–62%
L/W ratio: 1.35–1.5

Avoid: table below 50% or above 70%, depth below 50% or above 74%

Pear

Table: 53–63%
Depth: 58–62%
L/W ratio: 1.45–1.55

Avoid: table below 50% or above 70%, depth below 50% or above 74%

Marquise

Table: 53–63%
Depth: 58–62%
L/W ratio: 1.85–2

Avoid: table below 50% or above 70%, depth below 50% or above 74%

Heart

Table: 53–63%
Depth: 58–62%
L/W ratio: 0.95–1.02

Avoid: table below 50% or above 70%, depth below 50% or above 74%

Princess

Table: 67–72%
Depth: 64–75%
L/W ratio: 1–1.03

Avoid: table below 53% or above 85%, depth below 56% or above 84%

Cushion

Table: 61–67%
Depth: 61–67%
L/W ratio: Square 1.00–1.03, or rectangular 1.15–1.20

Avoid: table below 54% or above 73%, depth below 54% or above 73%

Emerald

Table: 61–69%
Depth: 61–67%
L/W ratio: 1.4–1.5

Avoid: table below 51% or above 79%, depth below 54% or above 79%

Asscher

Table: 61–69%
Depth: 61–67%
L/W ratio: 1–1.03

Avoid: table below 51% or above 79%, depth below 54% or above 79%

Radiant

Table: 61–69%
Depth: 61–67%
L/W ratio: 1.20–1.30, or square 1.00–1.03

Avoid: table below 51% or above 79%, depth below 54% or above 79%

Part 2 · Colour

White enough for its size

Colour is graded from D (colourless) to Z (light yellow). Neighbouring grades differ very little; what matters is whether you can see warmth face-up. That depends on two things:

Size. A small stone hides colour. The same H that looks white at 0.5 ct can look slightly warm at 2 ct.
Shape. Round brilliants hide colour best. Fancy shapes gather it at their tips, and step cuts (emerald, asscher) show it through their large open facets.

So we rate a colour grade against the stone’s size and shape. Grades that score Excellent and Very Good:

	under 0.50 ct	0.50–0.99 ct	1.00–1.99 ct	2.00 ct and up
Round	D–GH–I	D–GH–I	D–FG–H	D–FG
Oval, pear, marquise, heart, princess, cushion, radiant	D–GH–I	D–FG–H	D–FG–H	D–FG
Emerald, asscher	D–GH–I	D–FG	D–FG	D–FG

Fluorescence

A blue glow under UV light, usually harmless. Strong or very strong fluorescence can make a top-colour stone look slightly hazy, so it costs a few points. On I, J and K stones, blue fluorescence makes them look whiter, so there it costs nothing.

Tint

Some stones carry a brown, grey or green tint the colour grade doesn’t show. When the supplier reports one, we take points off: up to 18 for green, 12 for brown or grey.

Part 3 · Clarity

Clean to the eye

Clarity runs from FL (flawless) to I3 (heavily included). What matters for beauty is whether you can see anything without magnification. A well-placed SI1 can look exactly like a VVS1 from a normal viewing distance.

Larger stones have bigger facets, so inclusions are easier to spot, and step cuts are a grade stricter again because their open facets act like windows. Grades that score Excellent and Very Good:

	under 0.50 ct	0.50–0.99 ct	1.00–1.99 ct	2.00 ct and up
Round and brilliant shapes	FL–VS2SI1–SI2	FL–VS1VS2–SI1	FL–VVS2VS1–VS2	FL–VVS2VS1–VS2
Emerald, asscher	FL–VS2SI1	FL–VS1VS2	FL–VVS2VS1–VS2	FL–VVS2VS1

Eye-clean

When the supplier confirms a stone is eye-clean, it earns 5 extra points. A stone reported as not eye-clean loses 20.

Milky

A cloudy, hazy look that dulls the sparkle. Light milkiness costs 10 points, medium 20, and a heavily milky stone is rated Poor for clarity.

Lab

We take GIA, AGS, HRD and GCAL grades as printed. IGI is widely used and reliable but grades natural stones a little more generously, so natural stones graded by IGI lose 3 points. Lab-grown stones are compared with other lab-grown stones, where IGI is the standard.

Try it

Check a diamond

Copy the values from the certificate. Leave a box empty if it isn’t reported, and see what that does to the score.

Red flags

Walk away, or look very closely

Depth over ~70% on an oval, pear, marquise or heart

Weight hidden underneath. The stone faces up small and often shows a strong dark bow-tie.

Depth under ~56% on any fancy shape

Too shallow. Light passes straight through, leaving a washed-out “window” in the centre.

Extremely thin or very thick girdle

Thin edges can chip when the stone is set; thick ones hide carat weight you pay for but can’t see.

A milky or tinted stone

Brown, grey, green or hazy stones look dull whatever their grade says. Ask for a video in daylight.

Low clarity in a step cut

Emerald and asscher cuts show inclusions clearly. Below VS2 at 1 ct and up, look at the stone closely.

Numbers are a filter, not a verdict. They reliably catch badly cut stones, but two diamonds with the same numbers can still look different. Before you buy, look at a video of the actual stone, or ask us and we’ll review it for you.

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